iOS: Defer restoring screen mirroring until next runloop pass

Associating the UIWindow with a different screen will trigger layout
of the child views of the window, including the view that we're in
the process of removing, which doesn't have a platform window anymore.

Instead of protecting every possible code path in the view code
with checks for a platform window we defer the restoring of
mirror mode until after the view has been removed.

Pick-to: 6.2 5.15
Task-number: QTBUG-94530
Change-Id: I8c66106cafa67e06721e621c019b2d10acf02326
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

1 files changed, 7 insertions, 3 deletions

diff --git a/src/plugins/platforms/ios/qiosviewcontroller.mm b/src/plugins/platforms/ios/qiosviewcontroller.mm
index 7aeb3b9ca6..64d42d6b65 100644
--- a/src/plugins/platforms/ios/qiosviewcontroller.mm
+++ b/src/plugins/platforms/ios/qiosviewcontroller.mm
@@ -147,9 +147,13 @@
     UIWindow *uiWindow = self.window;
 
     if (uiWindow.screen != [UIScreen mainScreen] && self.subviews.count == 1) {
-        // Removing the last view of an external screen, go back to mirror mode
-        uiWindow.screen = [UIScreen mainScreen];
-        uiWindow.hidden = YES;
+        // We're about to remove the last view of an external screen, so go back
+        // to mirror mode, but defer it until after the view has been removed,
+        // to ensure that we don't try to layout the view that's being removed.
+        dispatch_async(dispatch_get_main_queue(), ^{
+            uiWindow.screen = [UIScreen mainScreen];
+            uiWindow.hidden = YES;
+        });
     }
 }